AuthorTopic: Factors influencing radio propagation (Read 74797 times)

Hi Heath. Please take a look at Celestial navigation forum. Topic is "Working the flight backwards". In particular reply #95 by Jeff Neville. His reply has a clear snapshot of why they turned south when they did. (the theory anyway).

I think in general that the general consensus is they went to far southof Howland, headed north on the LOP but turned back south just a bit too soon.

I've added a link to another Wikipedia article on "Radiation patterns." This is a basic introduction to antenna theory. It's also pretty "fundamental."

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I remain skeptical of the doughnut hole propagation pattern theory.

You seem to be difficulty understanding that signal strength does not vary smoothly with distance. As a general rule, that is how sound waves work: the stronger a sound is, the closer the source of a sound must be. If distance were the only variable, radio waves would work that way, too; but distance is not the only variable. The two articles given above suggest some of the other things that have to be considered.

If your implicit theory that all radio signals propagate in exactly the same way, regardless of frequency, time of day, antenna type, atmospheric conditions, or receiver location, then the radio operators of the Itasca would not have asked AE to stay on 3105 kcs.

Bob Brandenburg has not yet published his paper on the donut hole. I've kept him too busy working on underwater search technology.The donut hole is the result of an anomaly in the propagation pattern created by the Electra's transmitting antenna. Bob discovered it when applying an updated and more precise version of ICEPAC (Ionospheric Communications Enhanced Profile Analysis & Circuit) to the computer wire grid antenna model. In explaining it to me, Bob wrote:

"Out to 80 nmi. the 50% and 90% probability signals from the wire grid version are about the same as in the previous model. That's because of the steepness of the radiation pattern "skirt" at low radiation angles, and the "dimple" at the center of the pattern -- it's similar to the dimple in the upper half of an apple. But at greater distances the wire grid signal strength is considerably higher because the "skirts" of the pattern are steeper than in the previous version -- in which the pattern begins to curve inward at lower radiation angles. The difference is analogous to the difference between an apple with more vertical sides -- like a Washington Delicious -- and one with more roundish sides, like a Macintosh. The new mean value rises above the threshold at about 150 nmi, and stays above until 280 nmi. The 10%, and lower, probability curves stay above the threshold all the way out to 340 nmi. So there was a 50% chance Itasca could have heard Amelia when she was about 140 nmi away, a 10% chance of hearing her at 80 nmi, a 5% chance of hearing her at 60 nmi, and a 1% chance of hearing her at 40 nmi.

It's doubtful she was within 40 nmi of Howland, since that would put her within visual range of Baker Island if she was on the LOP. As for the maximum likely distance, it was possible -- at 10% or less probability -- that Itasca could have heard her even as she laid eyes on Niku."

In case you missed it in all that, Itasca had the best chance of hearing Earhart when she was between 150 and 280 nautical miles away. Obviously, this is a huge game-changer in any speculation about where she was at the time of the last in-flight transmission heard by Itasca. It knocks the Crashed & Sankers calculations of where they should be searching for a sunken aircraft into a cocked hat. Millions of dollars utterly wasted - even if the Electra crashed & sank at sea. If the airplane was south of Howland on the LOP, it was probably much closer to Gardner than has previously been thought likely. That puts it on the reef at Gardner much earlier and with more fuel remaining than previously thought possible. That, in turn, influences the credibility of the post-loss radio signals which required power from batteries recharged by running an engine.

Once Bob has had a chance to get his paper written and published, any skeptic with the ability and inclination to buy the software and check his calculations will be able to do so. Replication of results is the essence of scientific investigation.

AE appears to have had good two-way communication with Darwin for "200 miles" after departing for Lae.http://tighar.org/wiki/Receiver_fuse_replaced_in_DarwinI haven't found details, so don't know the shortest range of successful 2-way communication with Darwin. I don't know for sure what frequency she was using to talk with Darwin, although I remember reading it somewhere. Anyone know? Did she lose comms with Darwin when she switched frequencies, or just fly out of range (I also remember reading what frequencies were used, but can't find it now)? It would be nice to know her signal strength with Darwin, to compare with what the Itasca reported.

To Ric's point in reply #5. If she was closer to Gardner when she turned north on the LOP then that increases her flying time to Howland. It's likely then that she turned back south on the LOP just before coming upon Howland as Ric and others have suggested.

If AE was coming in strong (on the radio) at 150 to 240 miles out then how did she manage to drift so far right (south) of her course without FN catching it?

To be that far south it means their "drift" south of course had to be gradual and start much further back or she had to have changed course. If the drift south was constant then it should have been noticeable to FN much sooner so he could correct for it. Provided he could see stars for his plot. As AE continued to drift south then the ever widening difference between intended course and actual should have easily been noticed by FN and not accepted as being within "acceptable" plus and minus of his calculations. It almost feels like AE was on her own.

To be that far south it means their "drift" south of course had to be gradual and start much further back or she had to have changed course. If the drift south was constant then it should have been noticeable to FN much sooner so he could correct for it. Provided he could see stars for his plot.

And at 02:48 Itasca time, AP reporter Jim Carey heard her say "sky overcast." As Gary has often said, Noonan should have been able to find Howland using celestial methods but, as I have often said, he obviously didn't. Something, therefore, prevented Noonan from using celestial navigation. What might that something be?- Incapacitation (illness, dead drunk, fell out the door while trying to take a drift sighting)? Seems like AE would have mentioned something like that.- Dropped his octant? Almanac blew out the window?- Or how about something for which we have direct evidence - sky overcast.

As AE continued to drift south then the ever widening difference between intended course and actual should have easily been noticed by FN and not accepted as being within "acceptable" plus and minus of his calculations.

Not if he can't see the stars, and if he only gets a sun shot after the sun is up he has no way of knowing that he's south of course. I don't think we need to take Fred out of the equation to put them well south of course after a night of DRing with no check on what the wind is doing.

Thanks Ric. I wasn't trying to suggest he was out of the equation but your examples made me smile (Was the puff of smoke on takeoff in fact FN bailing out early? )

I know there was the sky overcast report from AE but for the whole trip? That's why I suggested FN should have caught this drift sooner. But if it's overcast, at night, and over water then AE is really flying by compass. No visual aids. Higher than expected winds aloft and now she drifts to the right. (what direction were the winds aloft?). FN then really was dead weight.

His sun sight at dawn then is the only "fix" he got? Just enough to establish his time to LOP? I know we don't know for sure but that's the suggestion?

AE appears to have had good two-way communication with Darwin for "200 miles" after departing for Lae.http://tighar.org/wiki/Receiver_fuse_replaced_in_DarwinI haven't found details, so don't know the shortest range of successful 2-way communication with Darwin. I don't know for sure what frequency she was using to talk with Darwin, although I remember reading it somewhere. Anyone know?

The old maxim for choosing a transmission frequency was, "the higher the sun, the higher the frequency."

"the radio transmission where AE says that Fred's almanac flew out the window"That occured during the takeoff from Lae. The almanac hit the ground in a puff of dust. Fred's sextant caused the other puff of dust, leaving him with an empty box and no way to navigate to Howland. 'Not sure what this has to do with radio propagation...

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